The present invention relates to balls, footballs, and other hand-thrown projectiles.
It is well-known that the proper way to achieve stable and accurate flight of a football is to impart rotation to it during launch. Many individuals find this difficult to achieve. Two prior footballs have been patented which include fins intended to impart rotation. These devices are discussed briefly below.
Thomas, U.S. Pat. No. 4,736,948, discloses an inflated football with a longitudinal central passageway containing angled internal fins. The present inventors have found that internal fins produce limited rotational torque due to two important factors. First, the fins are close to the center and thus have a short lever arm to impart torque upon the axis of rotation. Second, the air velocity through the central passageway is retarded by the friction and boundary layer of the passageway walls. Thus the fins' aerodynamic force, which is proportional to air velocity squared, is retarded.
Goldfarb, U.S. Pat. No. 3,225,488 discloses an inflatable football with four external tail fins. However Goldfarb oriented three of his four fins straight ahead so that they strongly resist the small amount rotational torque imparted by his slightly-angled fourth fin. Indeed, it has been determined that Goldfarb's football will not spin as well as an ordinary un-finned football.
There have also been footballs patented with spiral grooves or ridges to assist throwing. Some of these patents also state that the grooves or ridges impart rotation. Several of these balls have been tested by launching them free of initial rotation. None developed rotation in flight.